Conventional transmissions have been used for some time in different types of motor vehicles. The predominant construction method is the so-called countershaft construction method, in which the torque of an input shaft of the gearbox is transmitted to a countershaft and from there to an output shaft. Located on the shafts is a plurality of gearwheel trains corresponding to the number of gears. Each gearwheel train has at least one idler gear, which is mounted in a rotatable manner on a shaft, thereby enabling the simultaneous meshing of the gearwheel trains with different transmission ratios. When a gear is engaged, the idler gear of the corresponding gearwheel train is fixed in a torque-proof manner to the corresponding shaft by means of a coupling element, thereby enabling torque flow from the input shaft via the countershaft to the output shaft.
In order to enable the transmission of high torque with a small construction volume and low component costs, positive locking coupling devices, or as the case may be, clutches, are used almost exclusively. In order to change gears quickly, without shock, and with low noise and wear, it must be assured, when engaging a gear, that the parts to be connected in a torque-proof manner by means of the positive coupling device rotate at approximately the same rotational speeds. For this synchronization, small-dimension friction clutches can be used inside the transmission, whereby at least one separate clutch for synchronization is provided for each gear train.
The complexity and number of transmission components can, however, be reduced in that the synchronization is achieved by means of a corresponding adjustment of the ratio of the input speed to the output speed of the transmission. As the output shaft of the transmission is, as a rule, constantly connected in a drive-effective manner with the driven wheels of the motor vehicle, its rotational speed is determined by the driving speed of the motor vehicle. For that reason, the synchronization is usually done through the corresponding adaptation of the rotational speed of the input side of the transmission. If it is necessary to increase the speed of one shaft, as in the case of down-shifting, for example, this is implemented by means of the driving motor and the main clutch of the motor vehicle. For necessary deceleration of a shaft, a transmission brake is provided at least on the drive side of the drive train, within the transmission housing or immediately adjacent to the gearbox, which acts, for example, on the countershaft. When up-shifting, the transmission brake has the task of slowing the input side of the transmission to approximately the rotational speed of synchronization.
Unless expressly stated otherwise, the word clutch will be used below to designate a clutch that is located inside the gearbox, enables torque transfer between a shaft and an idler gear, and which usually, but not necessarily, is a positive clutch. In contrast, the clutch that implements torque transfer between the drive motor and the transmission, and which is usually shifted by means of a clutch pedal in motor vehicles with a manual transmission, is designated a main clutch.
The transmission brake can be actuated hydraulically, pneumatically, or electromagnetically. Even though an unregulated transmission brake might be sufficient in some cases, a transmission brake with adjustable braking force has considerable advantages in practice. This kind of transmission brake, for example, can be constructed as a brake that is actuated by two two-way valves, which are connected to the countershaft via a fixed transmission ratio.
While synchronization by means of a transmission brake can be easily implemented for automatic transmissions for motor vehicles, the functional principle of synchronizing transmission brakes can also be used for manual transmissions as well as for transmissions not used in motor vehicles.
A transmission brake is known from DE 196 52 916 A1. Here, a determined output rotational speed of the transmission and knowledge of the preselected transmission ratio are used to determine a target coupling rotational speed, and in cases where the target coupling rotational speed is lower than the determined actual rotational speed, a target braking gradient is determined and adjusted by means of valves. After the countershaft has reached the target coupling rotational speed via the braking action of the transmission brake, the gear is engaged and the brake disengaged. This solution is suitable for regulating the synchronization of normal shifting operations, however, with respect to regulation, is restricted to the minimum required basic function and by no means exhausts the technical possibilities of this kind of brake.
Against this background, the inventive task is to present a control method, or as the case may be, a regulating method, for a transmission brake, by means of which, without significant additional hardware expenses, the function of this brake can be significantly broadened. For purposes of linguistic simplicity, the term “control” will henceforth also encompass the term “regulation.” It will be obvious from the context whether control or regulation is meant, or it will be specified in the concrete configuration of this type of control.
The solution of this task is seen in the characteristics of the main claim, while advantageous embodiments and further developments of the invention will be apparent from the dependent claims.